The present invention is directed to an antenna arrangement for a diagnostic magnetic resonance apparatus for exciting and/or receiving magnetic resonance signals in or, respectively, from an imaging volume. An antenna conductor arrangement has at least first and second conductor sections. The conductor sections being connected to one another via a capacitor arrangement. During operation, the first conductor section exhibits an alternating first potential and the second conductor section exhibits an alternating, opposite, second potential relative to a reference potential. A shielding against electrical fields is arranged between the antenna conductor arrangement and the imaging volume.
In medicine, diagnostic magnetic resonance apparatus are employed, for producing tomograms of a patient or of a part of the patient. Different magnetic interactions of the different biological tissue are thereby interpreted, whereby the tissue is located in the imaging volume of the magnetic resonance apparatus. In the transmission case, an antenna arrangement generates high-frequency, spatially expansive magnetic fields. In the reception case, the same antenna arrangement or a special antenna arrangement receives the magnetic resonance signals emitted by the excited nuclei. The electrical fields that are always present with the high-frequency magnetic fields, however, are undesirable. In the reception case, the coupling of the electrical fields to the tissue under examination in the imaging volume leads to additional noise. In the transmission case, it leads to additional tissue heating and to a load-dependent detuning of the antenna arrangement.
German Published Application DE 43 14 338 A1 (corresponding to U.S. Pat. No. 5,410,251) discloses an antenna arrangement of the type initially cited wherein an electrical shielding is provided, which shields the electrical field generated by the antenna arrangement in the transmission case from the tissue and, conversely, electrically shields the antenna arrangement from the tissue in the reception case. The electrical shielding is implemented as a Faraday shield that is connected to a reference potential and is arranged between the antenna conductor and the imaging volume. Since the patient or the part of the patient to be examined in the imaging volume also assumes reference potential during operation of the magnetic resonance apparatus, electrical fields between the shielding and the patient are largely reduced. The expansive shielding of the antenna conductor by the Faraday shield, however, can also deteriorate the magnetic field. Further, the structural outlay is high because of the electrical leads to the reference potential that are required.
German Patent DE 43 01 557 C2, (Corresponding to U.S. Pat. No. 5,396,174 issued to Hanke et al.), discloses a Faraday shielding for a high-frequency antenna of a magnetic resonance apparatus that has little influence on the magnetic field component of the high-frequency field. This is achieved with a comb-like structuring of the Faraday shield.